Plant–soil feedback (PSF), regulated by both mycorrhizae and soil pathogens, is a primary mechanism maintaining high tree diversity in the tropics. But how warming may affect PSF is not well understood. We conducted warming experiments on seedling survival of a rhizobia-associated species (Ormosia semicastrata) carrying coevolved host-specific soil-borne pathogens and an ectomycorrhizal fungi-associated species (Cyclobalanopsis patelliormis) immune to soil-borne pathogens. We found elevated temperature lowered seedling mortality of O. semicastrata, but had no detectable effect on C. patelliormis seedlings. This indicates that warming weakened the negative PSF on O. semicastrata but did not affect the positive PSF on C. patelliormis. The differential warming effects on seedling mortality of species with different microbial associations imply that global warming could lead to change in tropical tree composition. Our study also predicts that global warming would undermine the role of the JC effect in maintaining tree species diversity in the tropics.

Forest soil CO2 efflux (FCO2) is a crucial process in global carbon cycling; however, how FCO2 respond to disturbance regimes in different forest biomes is poorly understood. We quantified the effects of disturbance regimes on FCO2 across boreal, temperate, tropical, and Mediterranean forests based on 1240 observations from 380 studies. Globally, FCO2 was increased by 13 to 25% due to climatic perturbations such as elevated CO2 concentration, warming, and increased precipitation. FCO2 was increased by forest conversion to grassland and elevated carbon input by forest management practices but was reduced by decreased carbon input, fire, and acid rain. Disturbance also caused changes in soil temperature and water content, which in turn affected the direction and magnitude of disturbance effects on FCO2. Our results suggest that disturbance effects on FCO2 should be incorporated into earth system models to improve the projection of feedback between the terrestrial C cycle and climate change.

Positive interactions have been hypothesized to influence plant community dynamics and species invasions. However, their prevalence and importance relative to negative interactions remain unclear, but are fundamentally important for both theoretical and applied ecology. We examined pairwise biotic interactions using over 50 years of successional data to assess the prevalence of positive interactions and their effects on each focal species (either native or exotic). We found that positive interactions were widespread and the relative frequency of positive and negative interactions varied with establishment stage and between native and exotic species. Specifically, positive interactions were more frequent during early establishment and less frequent at later stages. Positive interactions involving native species were more frequent and stronger than those between exotic species, reducing the impact of invasional meltdown on succession. Our study highlights the role of positive native interactions in shielding communities from biological invasion and enhancing the potential for long-term resilience.

The widespread observation that rare species have stronger conspecific plant-soil feedback (PSF) than common species raises more questions than answers on how rare species can possibly win the dance with abundant species. Here, we test soil feedback effect of phylogenetically related species on seedlings of contrasting local abundance in a subtropical forest. The results showed that although rare species suffered strong negative PSF in soils of conspecifics or phylogenetically close relatives, no such feedback was found in the soils of distant relatives. In contrast, although common species had weak conspecific PSF, they suffered consistently strong heterospecific soil feedback. These mechanisms ensure that rare species would fare well in the neighborhood of phylogenetically distant heterospecifics but do poorly under their close relatives, while common species perform relatively well in their own neighborhood but poorly in others’. This phylogenetic conservatism in PSF facilitates the persistence of rare species in a community.

1. The dissimilarity and hierarchy of trait values that characterize niche and fitness differences, respectively, have been increasingly applied to infer mechanisms driving community assembly and to explain species co-occurrence patterns. Here, we predict that limiting similarity should result in the spatial segregation of functionally similar species, while functionally similar species will be more likely to co-occur together either due to environmental filtering or competitive exclusion of inferior competitors (hereafter hierarchical competition). 2. We used a fully mapped 50-ha subtropical forest plot in southern China to explore how pairwise spatial associations were influenced by trait dissimilarity and hierarchy between species in order to gain insight into assembly mechanisms. We assessed pairwise spatial associations using two summary statistics of spatial point patterns at different spatial scales and compared the effects of trait dissimilarity and trait hierarchy of different functional traits on the interspecific spatial associations. These comparisons allow us to disentangle the effects of limiting similarity, environmental filtering and hierarchical competition on species co-occurrence. 3. We found that trait dissimilarity was generally negatively correlated with interspecific spatial associations, meaning that species with similar trait values were more likely to co-occur together and thus supporting environmental filtering or hierarchical competition. We further found that leaf area, wood density and maximum height had stronger trait hierarchy effects on the pairwise spatial associations relative to their corresponding trait dissimilarity effects, which suggests that hierarchical competition played a more (or at least equally) important role in structuring our forest community compared to environmental filtering. 4. This study employed a novel method to disentangle the relative importance of multiple assembly mechanisms in structuring co-occurrence patterns, especially the mechanisms of environmental filtering and hierarchical competition, which lead to indistinguishable co-occurrence patterns. This study also reinforced the importance of trait hierarchy rather than trait dissimilarity in driving neighborhood competition.